System for heating or air conditioning

ABSTRACT

A system for heating or air conditioning wherein provision is made for controlling fan speed and/or the heating and modulating valve in accordance with thermostat demand. The thermostat puts out a step function followed by a ramp for both on-off and proportional control. One valve may be used in series with another for each function. A logic gate is provided to override the speed control when the plenum is cold. Half speed is provided for a hot plenum even though there is no thermostat demand for heat. Two detectors are provided for plenum temperature. The same thermostat is used with both voltage sensitive and current sensitive circuits.

United States Patent 1 91 Sapir [54] SYSTEM FOR HEATING OR AIRCONDITIONING inventor: Said Sapir, Westlake Village, Calif.

Assignee: International Telephone and Tele graph Corporation, New- York,

. NZY. Filed: Jan,10,172

Appl. No.2 216,509

Related U.S. Application Data Division of Ser. No. 31,167, April 23,1970.

U.S. Cl.

References Cited '..165/26, 236/11 c Int. Cl 7 Field of Search ..165/25,26; 234/11 c UNITED STATES PATENTS Fmm Switch.

From

3/1970 Gerhart, Jr. et al. .....l65l26 3/1966 McGann T0 05 COUECIIDP[ll] 3,724,535 1 Apr. 3, 1973 Pfii rififiifi riiner iiharles SukaloAttorney-C. Cornell Remsen, Jr. et al.

[57] ABSTRACT A system for heating or air conditioning wherein provisionis made for controlling fan speed and/or the heating and modulatingvalve in accordance with thermostat demand. The thermostat puts out astep func- ;tion followed by a ramp for both on-off and propor- -tionalcontrol. One valve may be used in series with another for each function.A logic gate is provided to override the speed control when the plenumis cold. Half speed is provided for a hot plenum even though there is nothermostat demand for heat. Two detectors are provided for plenumtemperature. The same thermostat is used with both voltage sensitive andcurrent sensitive circuits.

1 Claim, 6 Drawing Figures ii/Air] will?? RH/lg PATENTEUAPR 3 ms SHEET 2[1F 5 PATENTEDAPM I975 SHEET 4 0F 5 increased thermostat demand.

SYSTEM FOR HEATING OR AIR CONDITIONING BACKGROUND OF THE INVENTION Thisinvention relates to temperature control systems and, more particularly,to heating or air conditioning units for offices, homes and the like.

In the past, use has been made of a bimetal-operated mechanical switchin a thermostat to control a gas furnace and associated blower.Normally, the blower and the gas are turned on when the ambient is toolow and turned off when it is sufficiently high.

The above-described on-off action has several sub stantialdisadvantages. In the first place, the one and off cycling causes unduewear on the equipment! The equipment further does not operateefficiently or economically in this manner. The blast of air isuncomfortable to people in the space where the blower is circulating theair. The on-off cycling also creates an ambient temperature which risesand falls with the cycle. The uneven character of the ambienttemperature is, thus, also uncomfortable to those occupying the heatedor cooled space.

Noise is also a problem. For example,with a large valve opening and ahigh velocity blower, the ducts will crack continually during heating bythe main burner,

cooled by the blower. Normally, the blower will not operate until theplenum temperature is high enough.

SUMMARY OF THE INVENTION In accordance with the present invention, theabovedescribed and other disadvantages of the prior art are overcome bycontrolling fan speed in accordance with thermostat demand.

A further feature of the invention is to provide a low minimum fire plusa gradually'increasing gas flow for Thus, it is seen that by varying fanspeed and fireintensity gradually, equipment performance, efficiency,and economy are improved. On-off cycling is reduced because of thegradual increase in fan speed and fire intensity. Air velocity isreduced and comfort is thereby increased. A more uniform and comfortableambient temperature is also produced because the control system of theinvention follows closely the departure of ambient from desired. Noiseis reduced because cycling is minimized.

It is another feature of the invention that certain gating logic isprovided, for example, to run the fan at half speed when the plenum ishot but the thermostat is no longer calling for heat. The half speed.is, thus, more comfortable.

' It is also a feature of the invention that two plenum temperaturedetectors are employed-one, to prevent an excessive burner run and theother, for fan control. Thus, one function is nottied to the other.

. and then will continue to crack when the plenum is supplies an amountof gas to burner 13 in proportion to V Still another feature of theinvention is the use of the same thermostat with a mode switch with botha heating and cooling system.

Still another feature of the invention resides in a solid statethermostat for producing a step function followed by a ramp forproducing both a sharp on-off signal and also a signal from which fanspeed and fire intensity may be proportioned to temperaturedifferential, i.e., set point minus ambient.

A further feature of the invention resides in the use of both currentand voltage sensitive circuits responsive to the self-same thermostatoutput.

Still a further feature of the invention resides in the use of twohalves in series, one of which can perform as an on-off, snap-actingvalve and the other of which can modulate gas flow according tothermostat demand. In this manner, more accurate proportioning can beachieved with a more positive gas shut off.

The above-described and other advantages of the in vention will bebetter understood. from the following description when considered inconnection with the accompanying drawings.

BRIEF DESCRIPTIONOF THE DRAWINGS DESCRIPTION o THE PREFERRED EMBODIMENTA heating system 10 is shown in FIG. 1, including a furnace ll having aheat exchange or plenum 12 which is heated by a main burner 13. Threevalves 14, 15, and 16 are connected in series in a gas pipeline 17 froma gas supply inlet to main burner 13. A thermocouple 18 is locatedadjacent a pilot burner, not shown, inside furnace 11 adjacent mainburner 13. As is conventional, failure of the pilot light will causevalve 14 to close through the failure of thermocouple 18 to supply anenergizing voltage.

Valve 15 is a snap-acting, on-off valve which receives an energizingsignal from a thermostat 26 shown in FIG. 2. Valve 16 receives aproportional control signal from a converter 20 shown in FIG. 2. Valve15 remains either completely closed or completely'open. Valve 16 Asshown in FIG. 2, valve 15 is tumed on and off by thermostat 26 operatingthrough a driver 21. Energization of valve 15 may be prevented either bya fault inhibitor 22 or a high limit inhibitor 23. Inhibitor 22 isactuated by a fault detector 24. inhibitor 23 is actuated by a highlimit detector 25.

Thermostat 26 supplies an output signal to a logic circuit 19, to onepole 27 of a selector switch 28, and to a gate 19. Logic circuit 19 alsoreceives an input from a low limit detector 29.

Selector switch 28 has a second pole 30 which 'is ganged with pole 27.Each pole has a heat, cold and off contact. Logic circuit 19 receivesanother input from thermostat 26'through the heat contact of pole 27over a lead 31, a lead 32, and a lead 33.

Converter receives the output of thermostat 26 from the heat contact ofpole 27. A driver 34 is connected from the cool contact of .pole 27 to acontrol relay 35. Cooling apparatus 36 is connected from relay 35.Driver 34 also supplies a control voltage to a fan speed control 37through the cool contact of pole 30. A fan switch 38 has a pole 39 withan on contact and an automatic contact. The on contact is connected tocontrol 37. The automatic contact is connected to pole 30. Pole 39 isconnected to control 37. Control 37 controls the speed of a fan 40. Fan40 is operated during both heating and cooling, although not necessarilycontinuously. Cooling apparatus 36 may simply be a compress'or or thelike. Fan 40 may, thus, circulate cool air as well as warm air. The samefan 40 may operate by circulating air in a heat exchanging relation withplenum 12. When poles 27 and are connected to the off contacts, nothinghappens. When poles 27 and 30 are connected to the heat contacts, thesystem will provide heating. When the poles 27 and 30 are'connected tothe cool contacts, the system will provide cooling. When pole 39 isconnected to the on contact, fan 40 will run at a constant speed all ofthe time independent of any other condition in the system. When pole 39isconnected to the automatic contact, control 37 may cause fan 40 to runat various speeds during heating. However, in accordance with theembodiment of the v present invention which is disclosed, the speed offan 40 is constant during cooling. Further, the amount of coolingprovided by apparatus 36 remains constant during the time that it isswitched on.

High limit detector 25 detects whether or not plenum 12 has atemperature above the predetermined level. Low limit detector 29 detectswhether or not the temperature of plenum 12 is below the predeterminedtemperature. The reference temperature of detectors 25 and 29 aredifferent, the reference temperature of detector 25 being higher thanthat of detector 29.

Both detectors 25 and 28 employ thermistors. Detector 24 detects thebreakage of the thermistor of detector 25.

Thermostat 26 produces an output voltage which varies with temperatureas indicated at 41 including a step at 42 at a critical temperature anda ramp at 43. The temperature at which step 42 is produced is manually'set in the thermostat 26. The ramp 43 is linear with, and thereforedirectly proportional to, the difference between the set temperature andthe ambient temperature.

Inhibitors 22 and 23 are, in effect, electronic switches in series witha power supply and valve 15. Thus, if either of the switches 22 or 23open, driver 21 cannot energize valve 15.

Converter 20 is a voltage-to-current convertersConverter 20, thus,converts with output voltage of thermostat 26 to a current proportionalto the voltage represented by curve 41. The amount that valve 16 opens,is then directly proportional to the temperature difference.

Logic circuit 19 operates gate 19. Gate 19 supplies a voltage to control37 which causes fan 40 to be driven at different speeds, depending upondifferent conditions. These conditions are as follows. When the outputof detector 29 indicates that plenum 12 is cold, the speed of fan 40 isreduced to zero. If the plenum is warm and thermostat 26 is calling forheat, the speed of fan 40 is directly proportional to the output ofthermostat 26. If plenum 12 is warm and thermostat 26 is not calling forheat, fan 40 is run at half speed, i.e., at a constant speed.

OPERATION If the thermistor of detector 25 should break, fault detector24 will cause inhibitor 22 to shut off valve 15 and thereby shut off allgas to main burner 13 as shown in FIG. 1. If plenum 12 is too hot,detector 25 will cause valve 15 to be shut off again by inhibitor 23.Otherwise, when the poles 27 and 30 are connected to the heat contacts,the system will operate as follows. When the ambient temperature fallsbelow the set temperature of thermostat 26, thermostat 26 will producean output starting with step function 42. This will cause valve 15 toopen. Converter 20 may also cause valve 16 to open a slight amount. Theplenum will then generally be cool and detector 29 will prevent fan 40from being turned on. If the ambient temperature begins to fall, theoutput of thermostat 26 will continue to increase as indicated at 43.Valve 16 will then be opened still further. When plenum 12 gets warm,logic circuit 19 will through gate 19' cause control 27 to rotate fan 40at a speed proportional to ramp 43. When thermostat 26 drops below theset point, valve 16 will be gradually closed and valve 15 will beabruptly closed at step function 42. If the plenum 12 is still hot,logic circuit 19 through gate 19 will cause fan 40 to be run at aconstant half speed until the plenum 12 cools.

In general, for very low heat demands, valve 15 may cycle briefly, andvalve 16 may not be turned on substantially. On the other hand, withrather a substantial demand, the system will operate continuously on theramp 43. When poles 27 and 30.are connected to the cool contacts,apparatus 36 and fan 40 will be cycled on and off in the conventionalmanner.

Driver 34 is an inverter. Provision is made to use the output of theself-same thermostat 26 for both heating and cooling.

It is also a feature of the invention that thermostat 26 puts out anoutput signal which changes in proportion according to curve 41. Thisself-same output is used directly in logic circuit 19 and control 37,whereas it is converted by converter 20 for control of valve 16.

Thermostat 26, detector 29, circuit 19, and gate 19' are shown in FIG.3. Thermostat 26 includes a bridge R51, R52, R55, and RTI-I3. R51, R52,and R55 are resistors. RTH3 is a thermistor located in plenum 12. Thethermostat may have resistor R55 calibrated in degrees for the settingthereof. Resistor R54 may be' employed to calibrate. the bridge. Thevoltage to the bridge is supplied by a resistor R50 and a zener diodeZ2. The output of the bridge is connected to an amplifier A1 having afeedback resistor R56 and a series feedback circuit including a diodeD20 and a resistor R58. A capacitor C12 is connected in parallel withresistor RS8. The point of forward and back bias of diode D20 producesthe step function 42. Amplifier A1 also has external connectionsincluding capacitors C10, C11, and resistor R57. The output ofthermostat 26 is provided on a lead 44. Lead 44 is connected to pole 27and to adiode D21 in gate 19. v

Dectector 29 includes a thermistor RTI-I2, resistors R21, R22, R23, R24,R25, R26, and R27. Transistors Q and Q11 operate substantially asbilevel devices with one emitter resistorR22. Transistor Q12 provides anoutput to gate 19 and feedback through diode D11 and resistor R26.

Circuit 19 includes transistors Q13 and Q14. Transistor Q16 in gate 19'operates as a switch so as to connect the heat contact of pole 30 (theinput to fan speed control 37) to ground when the plenum is cold.Transistor Q16 receives a control signal from detector 29 via resistorsR29 and R32. Circuit 19 also includes resistor R28, R30, and R31 anddiodes D12 and D14. Transistors Q13 and Q14 cause an output to fan speedcontrol 37 through the heat contact of pole 30 to hold the speed of fan40 at a half speed when the thermostat 26 is no longer calling for heatbut when the detector 29 indicates that plenum 12 is still hot.

Transistors Q13 and Q14 act as a logical or gate, and ground the base oftransistor Q15 either when the thermostat is calling for heat, or whenthe plenum is cold. When the plenum is hot and the thermostat is notcalling for heat, the base of transistor Q15 is biased at 6 volts whichruns the fan at half speed. Resistors R30 and R32 act as a voltagedivider to develop this bias,-a 16 volt supply being connected to oneend of resistor R30.

Diode D21 of gate 19' and diode D12 of circuit 19 prevents interferenceof one speed control circuit with the other. When diode D21 is backbiased, transistor Q15 supplies the half speed voltage. When diode D12is back biased, the thermostat signal provides a variable speed control.When transistor Q16 is turned on, re-

sistor R64 prevents the output of thermostat 26 to pole 27 from beinggrounded.

Detectors 24 and 25, inhibitors 23 and 22, driver 21, and valve 15 areshown in FIG. 4. Detector 24 includes resistors R1, R2, R3, R4 and R5, atransistor Q1, and a diode D1. Inhibitor 22 includes a resistor R15 anda transistor Q5. Detector 24 merely turns transistor Q5 off when valve15 should be de-energized.

Detector 25 is substantially identical to detector 29 including athermistor RTI-Il, resistors R6, R7, R8, R9, R10, R11, and R12, diodesD2 and D3, and transistors 02, Q3, and Q4. The output of detector 25 isimpressed upon a transistor Q7 in inhibitor 23 through resistor R13 anda resistor R14 in inhibitor 23. Detector 25 merely turns transistor offwhen valve 15 should be deenergized. Driver 21 includes an input circuitof resistors R16 and R48 with a diode D10. Driver 21 has an outputcircuit including a resistor 42 for the collector of a transistor Q6. Adiode D4 is connected in parallel with valve 15.

Converter and driver 34 are shown in FIG. 5. Converter 20 includes aninput resistor R17, an emitter resistor R18, a diode D23, and atransistor Q8. A diode D5 is connected in parallel with valve 16. Acircuit 45 may be provided, if desired, to adjust low fire. This circuitincludes resistors R65 and R66 and a transistor Q22. Converter 20produces an output current which may be similar to waveform 41 shown inFIG. 2 However, the pedestal and the ramp may both be variedindependently of the curve 41. The height of the pedestal may be variedby varying the resistance of resistor R18. The slope of the ramp may bevaried by changing the position of the wiper on potentiometer R66.

Driver 34 includes resistors R60, R61, R62, R63, and R19. Driver 34 alsoincludes a diode D22 and transistors Q25 and Q9. A diode D6 is connectedin parallel with the winding of relay 35. Driver 34 acts as an inverterfor the output of thermostat 26 received on a lead 46.

Fan speed control 37 is shown in FIG. 6. If switch pole 39 is moved tothe on contact, the control 37 receives a constant 16 volt input oninput lead 47. Otherwise, gate 19 supplies an input on lead 47 to causefan 40 to rotate at a speed proportional to the output of thermostat 26or to rotate at a constant half speed as explained previously. Control37 includes resistors R49, R33, R34, R35, R37, R38, R44, R45, and R47.Control 37 also includes transistors Q17, Q20, and Q18. Control 37 alsoincludes diodes D15, D13, D16, D17, D18, and D19. Control37 alsoincludes capacitors C3, C4, and C5. Control 37 also includes aunijunction transistor CR1 and a silicon-controlled rectifier CR3, atransformer T2, and inductor Lk, and a triac CR2.

Note will be taken that diodes D16, D17, D18, and D19 form a bridgerectifier. In order to obtain proper control of the current to fan motorM, it has been found that timing from zero current through triac CR2 isnecessary. Triac CR2 is similar to a silicon-controlled rectifier, butit may pass current in both directions depending upon the presence of a.signal on gate 48.

, When the current through triac CR2 goes to zero, the

diode bridge is energized to produce an output timing signal which isreceived by transistor Q7 over a lead 49 through resistor R33.Transistor Q17 throughtransistor 18 and diode D15 then causes capacitorC3 to charge through transistor Q9 to a potential substantially the sameas that impressed upon control 37 via lead 47. The speed control is thusa pedestal plus ramp. The pedestal is reached when capacitor C3 chargesrapidly at the beginning of the timing cycle. Capacitor C3 then chargesat a slower rate until unijunction transistor CR1 fires. Whenunijunction transistor CR1 fires, a triggering signal is impressed onthe gate of silicon-controlled rectifier CR3 via wire 45'. Thesilicon-con trolled rectifier CR3 then switches into conductioneffectively shorting the secondary 50 of the transformer T2 through thebridge D16, D17, D18 and D19. This causes gate 48 to open the triac CR2and allow it to pass current.

Note will be taken that the pedestal plus ramp varies the conductionangle of power input to the motor and therefore the motor speed. It is afeature of the invention that transformer T2 thus acts as abi-directional transmission device in that the starting signal for thetimer comes from the triac side of the circuit andthe conduction pulsefrom opposite side thereof, i.e., the low voltage side.

From the foregoing, it will be appreciated that one valve may besubstituted for both valves 15 and 16.

Further, the invention may be applied to air conditioning by itself, toheating by itself, or to both.

What is claimed is: V

1. In a system for heating and cooling, the combination comprising: athermostat for producing an output connect said thermostat either to aheating contact or to a cooling contact, said heating contact beingconnected to said first means; and an inverter connected from saidcooling contact to said second means.

1. In a system for heating and cooling, the combination comprising: athermostat for producing an output voltage proportional to thedifference between the temperature of the thermostat setting andambient; first means to vary the heat output of the system in accordancewith said voltage; second means to provide cooling; at least asingle-pole, double-throw switch to connect said thermostat either to aheating contact or to a cooling contact, said heating contact beingconnected to said first means; and an inverter connected from saidcooling contact to said second means.